COLUMBIA, S.C. (AP) — A splintered conservative vote in South Carolina could pave the way for Mitt Romney to win this week's pivotal primary — a contest due to have one fewer candidate after the withdrawal of moderate Jon Huntsman.

Huntsman, a former governor of Utah, will withdraw from the race Monday, campaign manager Matt David told The Associated Press on Sunday night. Huntsman will endorse Romney, aides said.

Before news of Huntsman's decision broke, Romney's other rivals wrestled with the likelihood that they'll split the vote of South Carolina's social conservatives.

"I think the only way that a Massachusetts moderate can get through South Carolina is if the vote is split," said Newt Gingrich, portraying himself as the lone conservative with a "realistic chance" of beating Romney in the first-in-the-South contest.

Polls show Romney, the former Massachusetts governor who struggled to a fourth-place finish in South Carolina during his 2008 White House run, with a lead heading into Saturday's vote. The state has a large population of evangelicals and other conservative Christians, and concerns arose four years ago about his Mormon faith.

But Gingrich, Rick Santorum and Rick Perry all said Romney, after victories in Iowa and New Hampshire, continued to benefit from the fractured GOP field and the failure of social conservatives to fully coalesce around a single alternative.

Santorum said South Carolina is "not going to be the final issue" and spoke of the "need to get this eventually down to a conservative alternative" to Romney. "When we get it down to a two-person race, we have an excellent opportunity to win this race," said the former Pennsylvania senator, who won the endorsement of an influential group of social conservatives and evangelical leaders Saturday in Texas.

Perry, the Texas governor, said it was "our intention" to compete in the next contest, Florida's Jan. 31 primary, even if he finished last in South Carolina.

Gingrich said he would "reassess" his candidacy if he lost in South Carolina and acknowledged that a Romney victory would mean "an enormous advantage going forward."

The former House speaker appealed for the support of "every conservative who wants to have a conservative nominee."

"I hope every conservative will reach the conclusion that to vote for anybody but Gingrich is, in fact, to help Romney win the nomination," he said.

The state's senior senator, Republican Lindsey Graham, started looking beyond Saturday's primary, saying, "If for some reason he's not derailed here and Mitt Romney wins South Carolina ... I think it should be over." He added, "I'd hope the party would rally around him if he did in fact win South Carolina."

To Rep. Tim Scott, R-S.C., the equation is simple: "If Romney wins South Carolina, I think the game's over. This is the last stand for many candidates."

He noted that three candidates are pursuing the evangelical vote "very strongly, and without any question that works to the Romney campaign's benefit. It's hard to find a single candidate that rallies all of the Christian voters in South Carolina, and therefore that splintered approach will probably have a major impact" in the primary.

Huntsman campaign officials said the candidate will withdraw from the race and endorse Romney at an event in Myrtle Beach, S.C. The former Utah governor placed third in last week's New Hampshire primary despite devoting most of his campaign resources to the state. He had already acknowledged that expectations for him in South Carolina's primary this week will be "very low."

Word of the Huntsman withdrawal came on the same day The State, South Carolina's largest newspaper, endorsed him for president.

Romney took a rare day off from campaigning while his opponents focused on the South Carolina coast.

Ron Paul returned to the state Sunday after spending three days at home and off the trail. The Texas congressman, whose libertarian message propelled him into second place behind Romney in New Hampshire, attended a rally in Myrtle Beach where he picked up the endorsement of a state senator popular with tea party members.

At the Cathedral of Praise in North Charleston, Gingrich was cheered by church members as he criticized activist judges who he said had made "anti-American" rulings to keep God out of schools. Santorum spoke at the same church Saturday.

At a prayer breakfast in Myrtle Beach, Perry appealed to religious conservatives to back his candidacy.

"Who will see the job of president as that of faithful servant to the American people, and the God who created us?" Perry said. "I hope each of you will peer into your heart and look for that individual with the record and the values that represent your heart."

The candidates faced a packed week of campaign events and nationally televised debates Monday and Thursday. No Republican has won the party's presidential nomination without carrying South Carolina.

Santorum battled Romney to a virtual tie in Iowa before falling to fifth place in New Hampshire. Gingrich and Perry fared poorly in both states.

All three have the backing of well-financed independent groups known as super political action committees that can help keep their candidacies afloat.

Santorum refused to suggest anyone should drop out of the race as a way to consolidate conservative support behind an anti-Romney candidate. But he said Republicans would have a hard time beating President Barack Obama in November if Romney were the nominee. Santorum cited Romney's push for mandatory insurance coverage in Massachusetts.

Gingrich and Perry used television interviews to focus on Romney's former leadership of the Bain Capital venture capital firm. Both defended raising questions about Bain's business practices, saying Romney's tenure would come under relentless assault from Democrats in the general election.

Gingrich, Graham and Scott appeared on NBC's "Meet the Press," while Santorum spoke on "Fox News Sunday" and Perry was interviewed on CNN's "State of the Union."

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Associated Press writers Tom Beaumont in Myrtle Beach, Julie Pace in North Charleston, Kasie Hunt in Charleston and Philip Elliott in Washington contributed to this report.